N-Acetyl KPV

1 Identity

Defined single synthetic tripeptide, N-alpha-acetylated and C-terminally amidated. Derived from residues 11-13 of alpha-MSH. Sold as 'N-acetyl KPV peptide powder (60 capsules)' by one seller.

Sequence

Ac-Lys-Pro-Val-NH2. The acetyl group is on the N-alpha (N2) amino group of the N-terminal lysine, not on the lysine N-epsilon side-chain amine, which remains free. The C-terminus is a primary carboxamide, not the free acid. Both statements are load-bearing and neither is inferable from the trade name.

Molecular formula

C18H33N5O4

Average mass

383.493 Da average, from the stated formula.

Monoisotopic mass

383.25325 Da monoisotopic neutral; [M+H]+ 384.26053.

Salt / variant note

Three collisions, in ascending order of difficulty. (1) plain KPV, H-Lys-Pro-Val-OH, C16H30N4O4, 342.44 Da, CAS 67727-97-3, already carried in the catalog - separated from this article by 41.05 Da and resolvable on any bench instrument. Not a real problem. (2) the name is wrong in the market. 'N-Acetyl KPV' strictly implies acetylation only, giving Ac-KPV-OH, C18H32N4O5, approximately 384.5 Da. What is actually shipped is the doubly modified Ac-KPV-NH2 at 383.49 Da. The two differ by 1.0 Da, which is not safely resolved at unit resolution and is easily masked by isotope-envelope misreading. (3) the hard one: N-alpha-acetyl and N-epsilon-acetyl KPV are positional isomers. Both are C18H33N5O4 at 383.49 Da, both have identical monoisotopic mass, and because the acetyl sits on the same residue in both, they give identical b/y fragment masses in MS/MS. Mass spectrometry alone cannot distinguish them. Also note the recurring market conflation of 'acetate salt' with 'acetylated', which are unrelated - one is a counterion and the other is a covalent modification, and at least one supplier's listing confuses them.

2 Class & testing panel

Form

Single article

Testing panel

P1 — panel definition

3 Primary sources & evidence

The index reports the design and provenance of the literature, not a conclusion about effect.

Identity settled; the formula is concordant between two suppliers and both masses follow from it. The positional-isomer problem is a general result of peptide analytical chemistry and is not in dispute.

4 Storage & specification

Storage

Lyophilized powder, -20 degrees C plus or minus 5 degrees C, desiccated, protected from light.

Shelf life

Provisional 24 months at -20 degrees C, assigned by protocol.